[libvirt] [v0.9.12-maint 8/9] Add support for using 3-arg pkcheck syntax for process (CVE-2013-4311)

[Eric Blake]

From: "Daniel P. Berrange" <berrange at redhat.com>

With the existing pkcheck (pid, start time) tuple for identifying
the process, there is a race condition, where a process can make
a libvirt RPC call and in another thread exec a setuid application,
causing it to change to effective UID 0. This in turn causes polkit
to do its permission check based on the wrong UID.

To address this, libvirt must get the UID the caller had at time
of connect() (from SO_PEERCRED) and pass a (pid, start time, uid)
triple to the pkcheck program.

This fix requires that libvirt is re-built against a version of
polkit that has the fix for its CVE-2013-4288, so that libvirt
can see 'pkg-config --variable pkcheck_supports_uid polkit-gobject-1'

Signed-off-by: Colin Walters <walters at redhat.com>
Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
(cherry picked from commit 922b7fda77b094dbf022d625238262ea05335666)
Signed-off-by: Eric Blake <eblake at redhat.com>

Conflicts:
	configure.ac - context
	libvirt.spec.in - context of indentation
	src/access/viraccessdriverpolkit.c - not present on this branch
---
 configure.ac    |  8 ++++++++
 daemon/remote.c | 22 +++++++++++++++++++---
 libvirt.spec.in |  3 +--
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/configure.ac b/configure.ac
index fa9d537..73a335e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1160,6 +1160,14 @@ if test "x$with_polkit" = "xyes" || test "x$with_polkit" = "xcheck"; then
   AC_PATH_PROG([PKCHECK_PATH],[pkcheck], [], [/usr/sbin:$PATH])
   if test "x$PKCHECK_PATH" != "x" ; then
     AC_DEFINE_UNQUOTED([PKCHECK_PATH],["$PKCHECK_PATH"],[Location of pkcheck program])
+    AC_MSG_CHECKING([whether pkcheck supports uid value])
+    pkcheck_supports_uid=`$PKG_CONFIG --variable pkcheck_supports_uid polkit-gobject-1`
+    if test "x$pkcheck_supports_uid" = "xtrue"; then
+      AC_MSG_RESULT([yes])
+      AC_DEFINE_UNQUOTED([PKCHECK_SUPPORTS_UID], 1, [Pass uid to pkcheck])
+    else
+      AC_MSG_RESULT([no])
+    fi
     AC_DEFINE_UNQUOTED([HAVE_POLKIT], 1,
         [use PolicyKit for UNIX socket access checks])
     AC_DEFINE_UNQUOTED([HAVE_POLKIT1], 1,
diff --git a/daemon/remote.c b/daemon/remote.c
index c65e4e4..2cdb079 100644
--- a/daemon/remote.c
+++ b/daemon/remote.c
@@ -2560,10 +2560,12 @@ remoteDispatchAuthPolkit(virNetServerPtr server ATTRIBUTE_UNUSED,
     int status = -1;
     char *ident = NULL;
     bool authdismissed = 0;
+    bool supportsuid = false;
     char *pkout = NULL;
     struct daemonClientPrivate *priv =
         virNetServerClientGetPrivateData(client);
     virCommandPtr cmd = NULL;
+    static bool polkitInsecureWarned;

     virMutexLock(&priv->lock);
     action = virNetServerClientGetReadonly(client) ?
@@ -2585,14 +2587,28 @@ remoteDispatchAuthPolkit(virNetServerPtr server ATTRIBUTE_UNUSED,
         goto authfail;
     }

+    if (timestamp == 0) {
+        VIR_WARN("Failing polkit auth due to missing client (pid=%lld) start time",
+                 (long long)callerPid);
+        goto authfail;
+    }
+
     VIR_INFO("Checking PID %lld running as %d",
              (long long) callerPid, callerUid);

     virCommandAddArg(cmd, "--process");
-    if (timestamp != 0) {
-        virCommandAddArgFormat(cmd, "%lld,%llu", (long long) callerPid, timestamp);
+# ifdef PKCHECK_SUPPORTS_UID
+    supportsuid = true;
+# endif
+    if (supportsuid) {
+        virCommandAddArgFormat(cmd, "%lld,%llu,%lu",
+                               (long long) callerPid, timestamp, (unsigned long) callerUid);
     } else {
-        virCommandAddArgFormat(cmd, "%lld", (long long) callerPid);
+        if (!polkitInsecureWarned) {
+            VIR_WARN("No support for caller UID with pkcheck. This deployment is known to be insecure.");
+            polkitInsecureWarned = true;
+        }
+        virCommandAddArgFormat(cmd, "%lld,%llu", (long long) callerPid, timestamp);
     }
     virCommandAddArg(cmd, "--allow-user-interaction");

diff --git a/libvirt.spec.in b/libvirt.spec.in
index 2e08abb..09272d4 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -364,8 +364,7 @@ BuildRequires: cyrus-sasl-devel
 %endif
 %if %{with_polkit}
 %if 0%{?fedora} >= 12 || 0%{?rhel} >= 6
-# Only need the binary, not -devel
-BuildRequires: polkit >= 0.93
+BuildRequires: polkit-devel >= 0.93
 %else
 BuildRequires: PolicyKit-devel >= 0.6
 %endif
-- 
1.8.3.1